1. Field of Invention
This invention relates to an improved integral ink filter for an ink jet printhead that has decreased flow resistance and minimal machine cost to implement. The integral ink filter includes both a first filter portion patterned in a silicon channel plate of the printhead and a second filter portion patterned in a polyimide layer located between the channel plate and a heater plate.
2. Description of Related Art Integral ink filters for inkjet printheads are known. Examples of such are U.S. Pat. No. 4,639,748 to Drake et al., U.S. Pat. No. 5,124,717 to Campanelli et al., U.S. Pat. No. 5,141,596 to Hawkins et al., and U.S. Pat. No. 5,204,690 to Lorenze, Jr. et al.
Of these, only U.S. Pat. No. 4,639,748 includes an integral, internal ink filter positioned within the channel plate before the individual ink channel nozzes. However, while its ink filter fabrication costs are small, it suffers an undesirable problem in that the filter pore open area is on the same order as the channel array density. Accordingly, such an ink filter induces significant ink flow resistance, which is detrimental to ink refill frequency.
The other cited references include a membrane filter fabricated over an ink fill opening between an ink supply cartridge and the ink manifold of the printhead (i.e., external to the channel plate and affixed to an outer face thereof). As such, these latter patents require additional fabrication costs and time to pattern and implement the ink filter assembly. Further, such a filter is quite removed from the nozzes.
Another known ink filter is the integral filter provided on the Hewlett Packard HP722 color printhead.
As technology moves towards smaller drop capability and thus increased resolution, there is a need for a better integral ink filter that can be fabricated with only minimal impact on manufacturing costs, while achieving a desired small pore size and decreased flow resistance.